1. Field of the Invention
The present invention relates to a magneto-resistance effect element.
2. Related Art
Since such a fact was found out that, when a current was caused to flow on a plane of a multi-layer film constituted of a ferromagnetic layer/a non-magnetic layer/a ferromagnetic layer, giant magneto-resistance effect (GMR) was developed, searching for systems having a further large magneto-resistance change ratio has been made. A ferromagnetic tunnel junction element (Tunneling Magneto-Resistance Effect element: TMR element) and a CPP (Current Perpendicular to Plane) type magneto-resistance effect element which causes a current to flow in a vertical direction to a film plane has been studied up to now, and these elements have been expected as reproducing elements for magnetic recording. Especially, the CPP type magneto-resistance effect element is a candidate for a reproducing element for a recording medium with a recording density of 200 Gbpsi or more, because it has a low resistance and a large MR ratio.
In a magnetic reproducing element using a CPP type magneto-resistance effect element, such a design is employed that a hard magnet is provided adjacent to a free layer for magnetic domain control on the free layer, and when a medium magnetic field does not serve, a magnetization direction of the free layer becomes approximately perpendicular to a magnetization direction of a pinned layer (for example, refer to JP-A-2001-312803).
In the CPP type magneto-resistance effect element, however, a current is caused to flow perpendicularly to a film face. Therefore, there is such a problem that, when a current with the same level as that in the CIP (Current In-Plane) type magneto-resistance effect element which allows a current to flow within a film plane is caused to flow in order to increase a reproducing output, a vortex magnetic domain occurs in the free layer due to a self-current magnetic field effect, which results in difficulty in magnetic domain control.
It is inevitable to perform stable magnetic domain control at an application time of a sense current with a high current density in order to achieve a further high reproducing output.
As described above, when it is desired that a large reproducing output signal is obtained using the conventional CPP type magneto-resistance effect element, there occurs such a problem that magnetization of the free layer becomes unstable. A finely machining process for device or element manufacture becomes difficult to perform according to a further ultra high densification, which results in increase in cost.